Increasingly popular online services (e.g., Twitter®, Facebook®, and Foursquare®) provide updated information from various users in a relatively short amount of time. Information available on these services is continuously generated and is far more time-sensitive than mostly static web pages. For example, breaking news appears and is propagated quickly by some of these online services, with new popular activities and hot topics arising constantly from real-time events in the physical world. Although each message or update may be small and contain limited textual content, a data stream may contain rich connections between users, topics, and messages, and these connections may be used to generate important social phenomenon.